The present invention generally relates to systems for testing of electronic devices, relates particularly to semiconductor reliability test systems for testing of electronic devices, and relates specifically to semiconductor reliability test systems for simultaneously testing of a plurality of electronic devices on a board.
In conventional burn-in ovens, multiple electronic devices were simultaneously tested together on multiple boards in a single cavity. As the DUTs and boards were different distances from the heat source, air was moved by fans inside of the cavity to evenly distribute the heat, with heat transfer to the DUTs being largely by convection. This resulted in several problems. First, moving air caused high pressure zones in the cavity which tended to force heated air out of the cavity and caused low pressure zones in the cavity which tended to draw outside ambient air in the cavity to replace the heated air which escaped. This results in uneven heat transfer rates and reduced operational efficiencies. Further, over time, the operation of the fan changed due to breakage and wear. Thus, even though designed and adjusted for optimal operation when leaving the factory, optimal operation was not continuously and indefinitely maintained over the life of the conventional oven in the field. Additionally, due to the continual influx of air, humidity of outside ambient air caused operational difficulties. When humidity posed a problem, conventional ovens were filled with dry nitrogen gas to replace the air in the interior and thus increasing operational costs.
Also, as multiple boards were in the same cavity, if it was desired to replace or modify one of the boards in the cavity, the door was opened to the cavity allowing heated air to escape and ambient air to enter the cavity. This exchange of air clearly had an effect on the conditions inside of the cavity and specifically of the remaining boards still under test. This effect was minimized if the door was opened and closed quickly but clearly never reduced to zero. Also, such exchange of air results in higher operational costs.
Further, typically the entire board was placed in the cavity with the other boards and electrical connections to the boards were made inside of the cavity. It can then be appreciated that in addition to the DUTs, the electrical connections to the boards were also heated every time that a test was performed. Heating of the electrical connections to the boards placed the electrical connections under thermal stress and resulted in reduced life and was a major cause of failure of the boards. This also results in higher operational costs. In addition, if it was necessary to remove one of the boards from the cavity, it was often necessary to reach inside of the cavity with high temperature tongs and attempt to grasp the board located inside of the cavity.
Further conventional ovens included a temperature sensor inside of the cavity and a temperature calibration device located outside the cavity. The temperature sensor and calibration device were calibrated together. The temperature sensor was generally located near the center of a cavity rather than adjacent the DUTs and measured the temperature of a large amount of moving air within the cavity rather than just the air adjacent to the DUTS. Thus, inaccuracies arose in temperature measurement which could affect the testing results. Also, due to the inaccuracies of temperature measurement, two ovens having identical temperature test settings did not necessarily have identical actual temperatures so that it was difficult to test the same DUTs in different ovens under identical conditions to compare test results. Also, in the event that the temperature sensor and/or calibration device should fail or otherwise lose their calibration, it was not possible to replace any failed component or to recalibrate in the field, but it was necessary to return the oven to the factory or like facility for recalibration.
Thus, a need exists for a system for simultaneously testing a plurality of electronic devices on boards which overcomes the disadvantages and deficiencies of prior burn-in and semiconductor reliability test systems.